Ink jet printer and drive method therefor

ABSTRACT

In an ink jet printer having pressure generate means for pressurizing ink inside the printer nozzles, either a first electric pulse of an amplitude enabling ink drop ejecting, or a second electric pulse of an amplitude lower than the amplitude of the first electric pulse for mobilizing ink inside a nozzle, is applied to each pressure generator synchronized to a reference signal of a single frequency. An ink drop is not ejected when a low amplitude second pulse is applied to a pressure generating means. Applying said second electric pulse instead stimulates ink around the nozzle so that high viscosity ink at the nozzle tip mixes with low viscosity ink deeper inside the nozzle, thereby lowering the overall viscosity of ink in the nozzle so that ink drop ejecting is easier.

FIELD OF THE INVENTION

The present invention relates to an ink jet printer for recording text,symbols, images, and other printing data by ejecting minute ink drops,and relates particularly to a control method for an ink jet printerwhereby clogging of nozzles by ink that has become more viscous in thearea of the nozzles is prevented.

RELATED TECHNOLOGY

Various methods of driving the nozzles of an ink jet recording device toeject recording ink from the nozzles have been disclosed and are todayused on such ink jet recording devices. These methods include using apiezoelectric element as the driving means as taught in Japan ExaminedPatent Publication (kokoku) 2-51734 (1990-51734); ejecting ink using aheating element for heating the ink as disclosed in Japan ExaminedPatent Publication (kokoku) 61-59911 (1986-59911); and ejecting ink fromthe nozzles by using an electrostatic actuator to vibrate a diaphragm bymeans of electrostatic force as disclosed in Japanese Patent Application(Tokkai) 7-81088.

Generally speaking, such ink jet printers buffer an image signal to RAMor other storage devices, and then selectively drive the appropriatepressure generating means, i.e., piezoelectric element, heating element,or electrostatic actuator, disposed near each nozzle to eject ink andprint to a recording medium based on the buffered image signal data.

A problem common to each of these ink jet printer designs is that whenink is not ejected from the nozzles for a certain period of time, inkaround the nozzles tends to dry due to evaporation of moisture or otherink solvent. This results in increased viscosity in ink near thenozzles.

When the viscosity of ink near the nozzles thus rises, the nozzles tendto clog, thus completely preventing ink from being ejected duringprinting, or preventing ink from being ejected at the normal dot sizeand speed. This increased ink viscosity can also slow the refill rate ofink to the nozzles, thereby preventing the nozzles from being refilledat the same rate ink is ejected. Air can become mixed with the ink whenthis happens, thus preventing ink drops from being ejected.

To avoid the above problems, many ink jet printers cover the nozzleswith a cap when printing (recording) is not in progress. This preventsthe nozzles from drying, and prevents an increase in the viscosity ofink around the nozzles.

In addition to such methods of covering the nozzles with a cap, manymethods of preventing ink blockage near the nozzles by regularlyejecting microdrops of ink from all nozzles separately from the printingprocess have also been proposed. These methods also help maintain andrecover printing performance.

Exemplary of these methods is the recovery process method disclosed inJapan Examined Patent Publication (kokoku) 6-39163 (1994-39163) forreliably expelling high viscosity ink without introducing air to thenozzles even when the viscosity of ink around the nozzles rises. This isaccomplished by setting the ink jet head drive frequency used during therecovery ejection operation lower than the highest drive frequency usedwhen recording text or images.

Methods other than expelling high viscosity ink to recover the nozzleshave also been disclosed. Exemplary of these is the method disclosed inJapan Unexamined Patent Publication (kokai) 56-129177 (1981-129177) forpreventing nozzle clogging due to dry ink around the nozzles by using anoscillator to vibrate the ink at the resonance frequency of the ink jethead and mobilize the ink when recording is not in progress.

The various methods described above, however, leave the followingproblems unresolved.

(1) Each of the above methods requires two drive frequencies, arecording frequency for ejecting ink drops during recording, and anozzle recovery frequency for driving a pressure generating means toprevent clogging, and these two frequencies must be used appropriately.The drive circuit and control thereof are thus complex.

(2) When an ink jet head having high viscosity ink around the nozzles isdriven at a frequency lower than a drive frequency used during normalrecording as taught in Japan Examined Patent Publication (kokoku)6-39163 (1994-39163), it can be difficult to expel high viscosity ink inink jet heads in which the pressure generated by the pressure generatingmeans is itself low. This method therefore cannot be used with all typesof ink jet printers.

(3) The viscosity also rises throughout the upstream ink path leading tothe nozzles, and not just around the nozzles, after a certain amount oftime has passed even if the ink is mobilized by vibrating the ink at theresonance frequency of the ink jet head when recording is not inprogress as taught in Japan Unexamined Patent Publication (kokai)56-129177 (1981-129177). Ink ejecting thus eventually becomesimpossible. As a result, this method cannot be used for applications inwhich normal ink jet recording is not performed for a certain period oftime, i.e., a no-ejection condition continues for a certain period oftime.

(4) When recording is not in progress the ink viscosity increases aroundall of the nozzles. During recording, however, fresh ink is constantlysupplied to frequently used nozzles and the ink viscosity at thosenozzles is therefore low while the ink viscosity around less frequentlyused nozzles increases. This means that both high viscosity and lowviscosity nozzles can be found in the same ink jet head duringrecording. While the less frequently used nozzles could be maintained byfrequent maintenance (recovery) ejecting therefrom, this necessitatesanalyzing the recording data to determine the no-ejection time for eachnozzle. This, however, is difficult to accomplish for each of the morethan one-hundred or so nozzles on an ink jet head. A method whereby allnozzles are regularly operated for nozzle recovery is therefore used onthe assumption that none of the nozzles has ejected once since the lastoperation. This method, however, results in the wasteful consumption ofink by frequently used nozzles, nozzles for which such nozzle recoveryejecting is not necessary.

An object of the present invention is therefore to provide an ink jetprinter whereby nozzle clogging can be reliably prevented by means of asimple method and construction, thereby resolving the above problems.

A further object of the present invention is to reduce the amount of inkconsumed by the recovery process for preventing nozzle clogging.

SUMMARY OF THE INVENTION

To achieve the above objects, a drive method for an ink jet printercomprising a plurality of nozzles for ejecting ink drops, pressuregenerating means disposed corresponding to said nozzles for pressurizingink in said nozzles, and a means for transporting said nozzles relativeto a printing medium for printing, generates a reference signal of asingle frequency, and applies to each pressure generating means of theink jet printer synchronized to the reference signal one of thefollowing: a first electric pulse of an amplitude enabling ink dropejecting, and a second electric pulse of an amplitude lower than theamplitude of the first electric pulse for mobilizing ink inside anozzle.

In addition, an ink jet printer having a plurality of nozzles forejecting ink drops, pressure generating means disposed corresponding tosaid nozzles for pressurizing ink in said nozzles, and a means fortransporting said nozzles relative to a printing medium for printing,comprises a reference signal generation means for generating a referencesignal of a single frequency, and a drive means for applying to eachpressure generating means synchronized to the reference signal one ofthe following: a first electric pulse of an amplitude enabling ink dropejecting, and a second electric pulse of an amplitude lower than theamplitude of the first electric pulse for mobilizing ink inside anozzle.

An ink drop is ejected from a nozzle for recording to a recording mediumwhen a first electric pulse is applied to a pressure generating means.Recording to a recording medium can thus be accomplished by selectivelyapplying the first electric pulse in a printing process according to theprinting content.

The first electric pulse is also used in a nozzle recovery process forpreventing nozzle clogging by ejecting ink drops from all nozzles.

When a second electric pulse of an amplitude lower than the amplitude ofthe first electric pulse is applied to a pressure generating means, anink drop is not ejected. Applying the second electric pulse mobilizesink near the nozzle, thereby stimulating ink around the nozzle so thathigh viscosity ink at the nozzle tip mixes with low viscosity ink deeperinside the nozzle. This lowers the overall viscosity of ink in thenozzle so that ink drop ejecting is easier.

The second electric pulse and first electric pulse are appliedselectively to pressure generating means synchronized to the samereference signal. Circuit configuration is thus simplified because aplurality of frequencies is not required, and control is thereforesimple.

The second electric pulse is used as follows in a nozzle recoveryprocess for preventing nozzle clogging. Specifically, the secondelectric pulse is applied a plurality of times to a pressure generatingmeans, and the first electric pulse is then applied. Applying the secondelectric pulse mobilizes ink in which there are localized increases inviscosity, notably near the nozzle. Mobilization thus lowers theviscosity of ink near the nozzle, and the first electric pulse is thenapplied to eject an ink drop from the nozzle. This sequence enablesreliable ink ejecting and nozzle recovery even in ink jet printers inwhich the pressure generated by the pressure generating means is low.

When a recovery process unit comprises applying the second electricpulse a plurality of times followed by applying the first electricpulse, it is also possible to perform a recovery process unit two ormore times consecutively.

The nozzle recovery process can be performed in a serial ink jet printerthat prints while moving the nozzles in a shift direction at eachprinted line, or after a print command is received and before a printingprocess based on the received print command. The nozzle recovery processcan also be performed at a regular interval during printer standbystates, or appropriately according to conditions.

The second electric pulse is used as follows during a printing process.

Specifically, a first electric pulse is applied selectively to pressuregenerating means according to the printing content to eject ink dropsfrom one or more nozzles, and the second electric pulse is applied tothose nozzles to which the first electric pulse is not applied. Thissuppresses an increase in the viscosity of ink in less frequently usednozzles. More specifically, this reduces differences in ink viscosityresulting from differences in the frequency of nozzle use in the sameink jet head. It is therefore possible to increase the interval betweennozzle recovery ejection operations, and thereby decrease wasteful inkconsumption from the nozzle recovery process. This method isparticularly effective in color ink jet printers where differences inthe frequency of nozzle use occur easily.

The method of the present invention can be used in any ink jet printerusing pressure generating means whereby ink drops can be ejected, or inkinside a nozzle can be mobilized without ejecting an ink drop, bychanging the amplitude of the drive pulse applied to a pressuregenerating means.

For example, the present invention can be used when the pressuregenerating means is an electrostatic actuator comprising a diaphragmthat is displaced by electrostatic force as taught in Japan UnexaminedPatent Publication (kokai) 7-81088 (1995-81088). As described in saidPublication, a residual charge accumulates in the diaphragm when apressure generating means of this type is driven for a prescribed time,and the relative displacement of the diaphragm tends to decrease. Byapplying a second electric pulse of polarity different from that of thefirst electric pulse, however, an increase in viscosity near the nozzlecan be prevented, and the residual charge can be simultaneously removed.

An ink jet printer having a plurality of nozzles for ejecting ink drops,pressure generating means disposed corresponding to said nozzles forpressurizing ink in said nozzles, and a means for transporting saidnozzles relative to a printing medium for printing, comprises accordingto a further embodiment of the present invention a common terminalconnected in common to each of said pressure generating means, aplurality of segment terminals connected individually to said pressuregenerating means, a first drive means for applying a first electricpulse to the common terminal, and a second drive means for applying asecond electric pulse of an amplitude different from the amplitude ofthe first electric pulse to a segment terminal. The difference betweenthe first electric pulse applied to the common electrode, and the secondelectric pulse applied to the segment electrode, is thus applied to apressure generating element. Each electric pulse is applied separatelyby the respective drive means to a pressure generating element. Asresult, electric pulses of two different amplitudes can be selectivelyapplied to a pressure generating element without complicated control.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an ink jet printer according to a preferredembodiment of the present invention.

FIG. 2 is a perspective view of an exemplary printing unit 90 shown inFIG. 1.

FIG. 3 is a cross-sectional view of an exemplary ink jet head 30 shownin FIG. 1.

FIG. 4 are plan views of the ink jet head 30 shown in FIG. 3.

FIG. 5 is a partial cross-sectional view used to describe the operationof the ink jet head 30 shown in FIG. 3, FIG. 5A showing the standbystate, FIG. 5B the ink intake state, and FIG. 5C the ink compressionstate.

FIG. 6 is a circuit diagram of one example of the selection means 150shown in FIG. 1.

FIG. 7 is a circuit diagram of one example of the driver 190 shown inFIG. 1.

FIG. 8 is a logic table showing the relationship between input signalsand output signals of the driver 190 shown in FIG. 7.

FIG. 9 is a timing chart of ink jet head operation during printing, andis used to describe an ink jet printer drive method according to apreferred embodiment of the present invention.

FIGS. 10A and 10B are flow charts used to describe an alternativeembodiment of an ink jet printer drive method according to the presentinvention.

FIG. 11 is a timing chart showing various signals used in the ink jetprinter drive method shown in FIG. 10.

FIG. 12 is a timing chart of ink jet head operation during a nozzlerecovery process according to an alternative embodiment of an ink jetprinter drive method according to the present invention.

FIG. 13 is a timing chart of ink jet head operation during a nozzlerecovery process in which a reverse polarity drive pulse is appliedaccording to an alternative embodiment of an ink jet printer drivemethod according to the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The preferred embodiment of an ink jet printer according to the presentinvention is described below with reference to the accompanying figures.

FIG. 1 is a block diagram of an ink jet printer according to a preferredembodiment of the present invention, and FIG. 2 is a perspective view ofan exemplary printing unit 90 shown in FIG. 1.

As shown in FIG. 1, an ink jet printer according to the presentinvention comprises a printing unit 90 and a control unit 100 forcontrolling the printing unit 90 based on an image signal transmittedfrom a host.

The printing unit 90 is comprised as shown in FIG. 2 and describedbelow. The recording paper 105 is transported by a platen 300, and inkis supplied to the ink jet head 30 through an ink supply tube 306 froman ink tank 301 in which ink is stored.

The ink jet head 30 comprises a pressure generating means such as apiezoelectric element, heating element, or electrostatic actuator, andis transported on a carriage 302. The carriage 302 is driven by a motor80 (FIG. 1), and moves in a direction perpendicular to thetransportation direction of the recording paper 105. A pump 303 has anink recovery process whereby ink from inside the ink jet head 30 isrecovered to a waste ink tank 305 by pumping the ink through a cap 304located at the recovery ejection position R and waste ink recovery tube308. It should be noted that this ink recovery process of the pump 303is used on ink jet heads which can no longer be refreshed by a recoveryejection process. This can occur when, for example, the ink jet printerhas not printed for an extended period of time, or when air becomestrapped in a nozzle.

The ink jet head 30 mounted on carriage 302 travels between printingarea P, which is approximately the same width as platen 300, and thefront of cap 304 (recovery ejection position R). The ink jet head 30ejects ink for recording when travelling through printing area P; therecovery ejection operation for preventing nozzle clogging is performedat recovery ejection position R.

The cap 304 can advance towards ink jet head 30 and retract from ink jethead 30. When ink is recovered from ink jet head 30, the cap 304advances to cover the nozzles of the ink jet head 30, and ink is ejectedfrom all nozzles of the ink jet head 30 into the cap 304. Recoveryejecting can be accomplished without covering the nozzles with cap 304when printing is in progress, and can be accomplished with the nozzlescapped when the ink jet printer is in a standby state.

The recovery ejection position R is also normally used as the homeposition of carriage 302. When the ink jet printer is powered on, thenozzles are covered by cap 304, and the ink jet head 30 waits at therecovery ejection position R until a print command is received.

A receive port 170 shown in FIG. 1 is a serial or parallelcommunications port for receiving an image signal from a host device.Image data contained in the image signal received through the receiveport 170 is stored to a print pattern storage means 110 such a randomaccess memory (RAM). When the print pattern storage means 110 is RAM,data stored to a memory address specified by a print operationcontroller (CPU) 200 using signals such as an address signal andread/write signal is sequentially read and output.

A recovery ejection data generator 160 generates data for recoveryejecting, i.e., generates the data used to drive and eject ink dropsfrom all nozzles, and outputs the data to a selector 150. The selector150 selects either the output of print pattern storage means 110 orrecovery ejection data generator 160, and passes the selected data tothe drive signal generator 180.

A drive signal generator 180 generates a drive data signal D1 to Dn foreach nozzle N1 to Nn based on the selected data output from the selector150. Drive data signal D1 to Dn defines the width and timing of thedrive pulse applied to the pressure generating means of each nozzle, andis output synchronized to a timing pulse output from the print operationcontroller (CPU) 200.

Memory 210 is RAM for storing print commands and other data containingin the image signal, and a read only memory (ROM for storing the programcontrolling other components. As a result, a print operation controller(CPU) 200 accesses the program stored in memory 210 to appropriatelycontrol the various components.

A counter 220 is a timer or similar device for counting the amount oftime following recovery ejecting. When a prescribed period has passed,the counter 220 outputs a time-up signal instructing output of therecovery ejecting signal, or sets a flag to indicate that a prescribedperiod has elapsed.

An ink jet head driver 190 boosts the drive signal output from the drivesignal generator 180 to drive the ink jet head 30. An other driver 195drives the motor 80. Operation of the motor 80 is controlled by acontrol signal from the CPU 200.

The drive voltage selector 130 selects the drive pulse applied to thepressure generating means of the ink jet head 30. The drive pulse iseither a high amplitude drive pulse causing ink drop ejecting, or a lowamplitude drive pulse for mobilizing ink inside the nozzles withoutejecting ink drops. The drive voltage selector 130 controls the ink jethead driver 190 to apply a high amplitude drive pulse to any nozzleoperated to eject ink for recording according to the drive signal outputby the drive signal generator 180, and to apply a low amplitude drivepulse to all other nozzles.

EMBODIMENT OF AN INK JET HEAD USED BY THE PRESENT INVENTION

FIG. 3 is a cross-sectional view of an ink jet head appropriate to thepresent invention, FIG. 4 is a plan view of said ink jet head, and FIGS.5A-5C partial cross sectional view thereof.

As will be known from the figures, this ink jet head 30 is a three layerstructure comprising a silicon nozzle plate 2 disposed on top of asilicon substrate 1, and a borosilicate glass plate 3 having a thermalexpansion coefficient substantially equal to that of silicon disposedbelow the silicon substrate 1 as shown in FIG. 3. Etched into thesurface (top surface as seen in FIG. 3) of the middle silicon substrate1 are recesses that function as a plurality of independent ink chambers5 and a common ink chamber 6 interconnected to each of the independentink chambers 5 by means of corresponding ink supply paths 7. It shouldbe noted that the formation of ink chambers 5, common ink chamber 6, andink supply paths 7 is completed by covering the recesses, i.e., thesurface of silicon substrate 1, with the nozzle plate 2.

A plurality of nozzles 11 is formed in the nozzle plate 2 at a positioncorresponding to an end part of each ink chamber 5. Each nozzle 11 isopen to the corresponding ink chamber 5. An ink supply opening 12 opento common ink chamber 6 is also formed in nozzle plate 2. Ink issupplied from ink tank 301 (FIG. 2) through ink supply tube 306 (FIG. 2)to charge the common ink chamber 6 through ink supply opening 12. Theink charge in common ink chamber 6 is then supplied through ink supplypaths 7 to the corresponding independent ink chambers 5.

The bottom wall 8 of ink chamber 5 is thin, and functions as a diaphragmthat can be flexibly displaced up and down as shown in FIG. 3. Thisbottom wall 8 part of ink chamber 5 is therefore alternatively referredto in the following description as diaphragm 8.

The surface of borosilicate glass plate 3 bonded in contact with thebottom of silicon substrate 1 is also etched to form a plurality ofshallow recesses 9 at positions corresponding to the ink chambers 5 insilicon substrate 1. The bottom wall 8 of each ink chamber 5 thereforeopposes the surface 92 of corresponding recess 9 with an extremelynarrow gap therebetween. A surface projection 92 b projecting fromsurface 92 toward bottom wall 8 is provided on the surface of recess 9in the area of nozzle 11. As a result, the gap between surfaceprojection 92 b and bottom wall 8 b is less than the gap at other areasbetween surface 92 and bottom wall 8 a.

The bottom wall 8 of each ink chamber 5 functions as an electrode forstoring a charge. A segment electrode 10 is formed on recess surface 92of glass plate 3 in a position opposite bottom wall 8 of each inkchamber 5. The surface of each segment electrode 10 is covered by aninorganic glass insulation layer 15 of thickness G0 (see FIG. 5). As aresult, each segment electrode 10 and the corresponding ink chamberbottom wall 8 form opposing electrodes having an insulation layer 15disposed therebetween and an electrode gap that varies according to thelocation. More specifically, the electrode gap between these opposingelectrodes is a distance G2 near the nozzle, and a distance G1 in otherareas.

As shown in FIG. 4, ink jet head driver 190 charges and discharges theopposing electrodes according to the control signal output from the CPU200 and the drive signal output from drive signal generator 180. Thedriver 190 outputs directly to each segment electrode 10, and directlyto a common electrode terminal 22 formed on silicon substrate 1.Impurities injected to silicon substrate 1 are conductive, enablingcommon electrode terminal 22 to supply a charge to bottom wall 8. Whenit is necessary to supply a voltage to the common electrode with lowerresistance, a metallic thin-film or other conductive material can beformed on one surface of the silicon substrate 1 by such methods asvapor deposition or sputtering. The silicon substrate 1 and borosilicateglass plate 3 are bonded in the present exemplary embodiment by anodicbonding, and a conductive film is therefore formed on the same surfaceof the silicon substrate 1 as the ink path is formed.

A cross sectional view of the ink jet head through line III—III of FIG.4 is shown in FIG. 5. When a drive voltage is applied from driver 190 toopposing electrodes, Coulomb force is produced in the opposing electrodegap, thus displacing the bottom wall (diaphragm) 8 toward segmentelectrode 10 and increasing the capacity of the ink chamber 5 (see FIG.5B). When the driver 190 then causes the charge stored in the opposingelectrodes to rapidly discharge, the elastic restoring force of thebottom wall 8 causes the bottom wall 8 to return to the original staticposition, thereby rapidly compressing the capacity of the ink chamber 5(FIG. 5C). The pressure thus generated inside the ink chamber causespart of the ink charge in ink chamber 5 to be ejected as an ink dropfrom the nozzle 11 corresponding to that ink chamber.

As described above, however, the opposing electrode gap is formed withboth a small gap G2 and a large gap G1. It is therefore possible todisplace bottom wall 8 bof diaphragm 8 located at small gap G2 to theopposing wall of surface projection 92 b by applying a smaller drivevoltage than is needed to displace bottom wall 8 a at the large gap G1.

Two vibration modes can therefore be achieved by appropriately applyinga high drive voltage causing displacement of the entire diaphragm towardopposing wall surface 92, and a low drive voltage causing displacementof only diaphragm bottom wall 8 b at small gap G2. The vibration modeachieved by applying a high drive voltage causes diaphragm 8 to vibratesufficiently to eject an ink drop, and the vibration mode achieved byapplying a low drive voltage produces diaphragm vibrations mobilizingink around the nozzle.

DRIVE CIRCUIT

An exemplary embodiment of a drive circuit according to the presentinvention is described next below with reference to FIGS. 6 to 8. FIG. 6is a circuit diagram of a preferred embodiment of a selector 150 shownin FIG. 1, and FIG. 7 is a circuit diagram showing the major componentsof a driver 190 comprising a drive voltage selection means.

Referring to FIG. 6, a receive buffer 110 functions as the print patternstorage means shown in FIG. 1. Based on drive data signal D1 to Dnoutput from the selector 150, a drive pulse signal generator 180 appliesa drive signal to each nozzle N1 to Nn. It should be noted that receivebuffer (print pattern storage means) 110, selector 150, and drive pulsesignal generator 180 can be integrated into a single gate array.

Receive buffer 110 stores one column of print data, outputs the data ata latch signal from the print operation controller (CPU) 200, and thenobtains the next data set from the preceding stage.

As shown in FIG. 6, selector 150 comprises two AND elements 152 and 153and one OR element 154 per nozzle. Based on a selection signal Se 161output from the CPU 200, the selector 150 selects either print dataoutput from the receive buffer 110, or recovery ejection data producedby recovery ejection data generator 160, and outputs to drive pulsesignal generator 180.

the selection signal Se is low, NOT element 151 outputs high, resultingin a high input to AND element 152. As a result, the print data suppliedfrom the receive buffer 110 to the other input of AND element 152 issent to the drive pulse signal generator 180. When the selection signalSe 161 is high, the data from the receive buffer 110 is not output tothe drive pulse signal generator 180, and the recovery ejection data issent to the drive pulse signal generator 180. As a result, the data sentto the drive pulse signal generator 180 results in periodic ink dropejecting from all nozzles.

A timing pulse Tp of a prescribed pulse width is applied to one input ofeach NAND element 181 of drive pulse signal generator 180. Data signalD1 to Dn output from selector 150 is inverted by NOT element 182, andthe inverted data signal is applied to the other input of each NANDelement 181.

The ink jet head driver 190 comprises a driver 190 a for driving thecommon electrode terminal 22 (diaphragm 8) side of the ink jet head, anda driver 190 b for driving each segment electrode 10 based on the drivedata signal D1 to Dn. Driver 190 a switches the voltage applied to thecommon electrode terminal 22 between a voltage V1 and the ground (0 V);driver 190 b switches the voltage applied to the segment electrode 10between a second voltage V2 and the ground (0 V). Note that V1 isgreater than V2, and two different voltages, V1 and V1-V2, (or threevoltages if 0 V is included) can be applied to the opposing electrodegap (between the diaphragm 8 and segment electrode 10).

Driver 190 a comprises primarily transistors Q1 and Q2, and resistancesR1 and R2. The timing pulse Tp is applied to the input terminal of thedriver 190 a. When the timing pulse Tp switches to the on state (high),transistor Q1 is on, and voltage V1 is applied to common electrodeterminal 22. When the timing pulse Tp is off (low), transistor Q1 isoff, transistor Q2 is on, and the common electrode terminal 22 isconnected to the ground (0 V).

The other driver 190 b comprises a plurality of circuits comprisingprimarily transistors Q3 and Q4 and resistances R3 and R4. Note that thenumber of these circuits matches the number n of segment electrodes 10.Each input terminal of driver 190 b is connected to an output terminalof drive pulse signal generator 180. When data Dx for an X-th nozzle 11x goes high, i.e., when an ink drop is to be ejected from nozzle 11 x,and timing pulse Tp goes on (high), transistor Q4 goes on and thecorresponding segment electrode 10 x is connected to the ground (0 V).

When data Dx for nozzle 11 x goes low, i.e., when an ink drop is not tobe ejected from nozzle 11 x, and timing pulse Tp goes on (high),transistor Q3 goes on and voltage V2 is applied to the correspondingsegment electrode 10 x.

A logic table showing the relationship between the timing pulse Tp, datasignal Dx, and the potential of the opposing electrodes is shown in FIG.8. As will be known from this table, when timing pulse Tp and datasignal Dx are both high, the potential difference between the opposingelectrodes is V1. Charging thus causes the entire diaphragm 8 to bedisplaced toward the segment electrode as shown by state (1) in FIG. 8.When the timing pulse Tp goes low from this state, the opposingelectrodes become equipotential, the stored charge is discharged, andthe diaphragm 8 returns to the original non-displaced position. Thisproduces pressure inside ink chamber 5, which causes an ink drop to beejected from nozzle 11 (state 2).

When the timing pulse Tp is high and data signal Dx is low, thepotential difference of the opposing electrode gap is V1-V2, and thediaphragm 8 is displaced only in the area of the segment electrode area10 b (state 3). When the timing pulse Tp then goes low from this state,the opposing electrode gap again becomes equipotential, the storedcharge is discharged, and the diaphragm 8 returns to the originalnon-displaced position. In this case, however, the amplitude ofdiaphragm 8 vibration is smaller than when the diaphragm 8 returns fromthe state (1) position to the state (2) position. The pressure insidethe ink chamber 5 therefore does not rise sufficiently to eject an inkdrop from the nozzle 11, and vibration of diaphragm 8 results only inmobilizing ink around the nozzle 11.

The operation of the circuits comprised as above is described next belowwith reference to the timing chart shown in FIG. 9.

For printing, the selection signal Se output from the CPU 200 is low. Alatch signal 120 from the CPU 200 sets the column print data read intoreceive buffer 110 to the drive pulse signal generator 180. Theselection signal Se from the CPU 200 remains low while printingcontinues, thereby steadily supplying the column print data to the drivesignal generator 180 and therefrom to the driver 190.

The timing pulse Tp input to drivers 190 a and 190 b is a periodic pulseof period T and pulse width Pw as shown in FIG. 9. The time from thestart of opposing electrode gap charging to the start of discharging isdetermined by pulse width Pw.

The motor 80 for transporting carriage 302 is driven synchronized totiming pulse Tp, and the input of latch signal to the receive port issynchronized to timing pulse Tp.

Based on the print data, the data signal Dx input to the drive pulsesignal generator 180 is output high synchronized to the timing pulse Tpwhen an ink drop is to be ejected. The data signal Dx is thereforesequentially output high-low-low when dot 1 is printed and dots 2 and 3are not printed as shown in FIG. 9. This results in drive pulses ofpulse width Pw and amplitude V, V1-V2, and V1-V2 being sequentiallyapplied to the opposing electrode gap. This sequence of drive pulsescauses ink drop ejecting at dot 1, and ink mobilization around thenozzle without ink drop ejecting at dots 2 and 3.

The simple circuit configuration of the present invention can thus applya low amplitude drive pulse to non-ejecting nozzles only to mobilize inkaround the nozzle and prevent a rise in the viscosity of ink around thenozzle while printing is in progress, and can accomplish this withoutcomplicated control. It is therefore possible to suppress a rise in theviscosity of ink in infrequently used nozzles. This means thatdifferences in viscosity at the nozzle tip resulting from differences inthe frequency of nozzle use can be reduced, the interval between nozzlerecovery operations can be increased, and wasteful consumption of inkduring nozzle recovery can be reduced. The method of the presentinvention is particularly effective in the case of a color ink jetprinter having a plurality of nozzles grouped by color because anoticeable difference in the frequency of nozzle use occurs easily withsuch printers.

Latch signal output from the CPU 200 stops and the printing process isinterrupted during the nozzle recovery process. The ink jet head 30 isthen moved to the recovery ejection position R, selection signal Se isset high, recovery ejection data causing all nozzles to ejectperiodically is set to the drive pulse signal generator 180, and allnozzles are thus operated to eject plural times.

If all data signals are held low and timing pulse Tp is applied whileink jet head 30 is moved to the recovery ejection position R, a rise inthe viscosity of ink around the nozzle can be suppressed by applying alow amplitude drive pulse causing mobilization of ink near the nozzle.

It should be noted that an exemplary drive circuit according to thepreceding embodiment of the present invention has been described drivingan ink jet head comprising an electrostatic actuator as a pressuregenerating means. The invention shall not be so limited, however, andthe same effect can be achieved in ink jet heads in which apiezoelectric element, heating element, or other type of pressuregenerating means is used. More specifically, the present invention canapply two drive pulses of different amplitudes to such other types ofink jet heads. Displacement varies according to the voltage of theapplied drive pulse when a piezoelectric element is used, and ink aroundthe nozzle can therefore be mobilized without ink ejecting. The amountof heat generated likewise varies with a heating element, and a lowamplitude drive pulse can therefore again be used to mobilize ink aroundthe nozzle without ink ejecting.

PREFERRED EMBODIMENT OF A CONTROL METHOD

A preferred embodiment of an ink jet printer control method according tothe present invention is described next below with reference to the flowcharts in FIG. 10. Note that the main routine is shown in FIG. 10A, anda subroutine is shown in FIG. 10B.

When the printer power is turned on, the control unit 100 and printingunit 90 are initialized (step SO). Recovery process A is thenaccomplished (step S1) to expel any ink that had become more viscousduring the period of printer non-use. Recovery process A applies suctionto the capped nozzles using pump 303, and by this action removes inkthat had become too viscous to eject from the nozzles.

It should be noted here that recovery process B described below differsfrom recovery process A in that it applies a drive pulse to the pressuregenerating means to expel by forcing out from the nozzle ink that hadincreased in viscosity near the nozzle.

After recovery process A is completed, counter 220 is reset and beginscounting a prescribed period. This counting operation is used todetermine the passage of a required minimum period, and to count thetime elapsed from that minimum period. Output of a time-up signal isthen detected (step S2) to determine whether the counter 220 has countedthe prescribed time, that is, whether the prescribed period has elapsed.If the time-up signal is detected, recovery process B is performed (stepS8).

Recovery process B is shown as subroutine (b) comprising steps SS1 toSS3 in FIG. 10. This subroutine starts by moving carriage 302 carryingink jet head 30 to the home position, which is recovery ejectionposition R (step SS1). Recovery ejecting (step SS2) then expelsincreased viscosity ink from all nozzles into the cap. Ink is generallyejected anywhere from several to several hundred times per nozzle toexpel any defective, increased-viscosity ink from the nozzles. Afterejecting, the carriage is returned to the position from which it wasmoved to the recovery ejection position R (step SS3) to completerecovery process B.

It should be noted that if the carriage is already positioned at therecovery ejection position R when the time-up signal is output, it isobviously not necessary to move the carriage (step SS1 can be skipped)before recovery ejecting in step SS2, and it is not necessary to movethe carriage when recovery ejecting is completed (step SS3 can beskipped). Thus, it is sufficient to simply eject ink from the nozzleswhile the nozzles remain capped.

It should be further noted that the number of ink expulsionsaccomplished in recovery process B is determined in this embodiment by aprescribed time counted by counter 220.

If in step S2 the time-up signal is not detected, it is determined (stepS3) whether printing is to be accomplished. If printing is notrequested, step S3 loops back to step S2.

If a print command signal has been received from a host device andprinting is requested, recovery process B is performed (step S4), andthe counter 220 is then reset (step S5). After the printing process isthen accomplished (step S6), the carriage is returned to the homeposition (step S7), and the nozzles are capped. If the power is still on(step S9), the procedure then loops back to step S2. If the power is off(step S9), the procedure terminates.

As thus described, a recovery process A using a pump to purge thenozzles is first accomplished when the power is turned on. Thereafter, arecovery process B to recover the nozzles by ejecting is performedimmediately before printing commences and at a prescribed regularinterval when printing is not performed.

It should be further noted that after recovery process A, the controlmethod of the present invention applies a low amplitude drive pulse toall nozzles when not printing, and to the non-ejecting nozzles whenprinting, to constantly mobilize ink near the nozzles. As a result, thefrequency of recovery process B can be reduced, and ink waste can beprevented, when compared with methods which do not apply this type ofdrive pulse.

FIG. 11 is a timing chart of various signals used to achieve theembodiment of the invention described with reference to FIG. 10.

Signal 40 a indicates the power supply state; 40 b indicates the countof the counter 220, that is, the timer signal. The dot-dash line 40 findicates the time-up time counted by the timer signal 40 b. The timersignal 40 b is indicative of a particular value such as time or a clockcount. The time-up signal 40 c is output by the counter 220 when theprescribed time is up. The print signal 40 d is received through receiveport 170. The recovery process signal 40 e is output appropriately bythe CPU.

When the CPU receives time-up signal 40 c and print signal 40 d, itinstructs the various means shown in FIG. 1 to perform the recoveryprocess according to the procedure of the flow chart shown in FIG. 10.

When the power supply is turned on a41, recovery process A is performed(e31). If the print signal 40 d is not received and the printertherefore does not print within a prescribed time, the time-up signal 40c is set high to a time-up state c41. This causes recovery process B(e42) to be performed. Soon thereafter when printing occurs d41, theprint signal 40 d causes the counter 220 to be reset and the recoveryprocess B (e51) to be performed. If the print signal 40 d is thereafternot detected for a sufficiently long period, the recovery process B isrepeated (e43, e44, e45) each time the time-up signal 40 c indicates theprescribed time has elapsed (c42, c43, c44).

It should be noted that if the time-up time 40 f is short, the nozzlerecovery process will be performed frequently, ink consumption willtherefore increase, and the amount of ink available for printing willthus decrease. As a result, the print capacity (number of printablecharacters) per head or cartridge decreases. Conversely, if the time-uptime 40 f is too long, the amount of unusable ink in the nozzlesincreases, and the amount of ink that must be ejected in recoveryprocess B immediately before printing increases.

As described above, however, the control method of the present inventioncauses a low amplitude drive pulse to be applied to all nozzles duringnon-printing times to mobilize ink around the nozzles. When comparedwith methods in which such a drive pulse is not applied, the method ofthe present invention can therefore set the time-up time 40 f to alonger time without increasing the ink volume ejected during recoveryprocess B. More specifically, the control method of the presentinvention can decrease the frequency of the nozzle recovery process andthereby prevent ink waste.

As also described above, the method of the present invention uses atime-up signal 40 c output by a counter 220, and a print signal 40 dreceived from a host device, as triggers for initiating the recoveryprocess B. It will be obvious, however, that it is also possible to useonly one of these signals as the trigger for recovery process B. Forexample, the time-up signal could be used as a trigger for recoveryprocess A, and only the print signal could be used as a trigger forrecovery process B. In this case, recovery process B could be performedto eject ink several ten times preceding a printing process when a printsignal is received from a host, recovery process B could be performed toeject several times after printing a prescribed number of lines, andrecovery process A could be triggered by the time-up signal.

PREFERRED EMBODIMENT OF A DRIVE PULSE FOR A NOZZLE RECOVERY PROCESS

FIG. 12 is a timing chart of an exemplary drive pulse used for a nozzlerecovery process according to the present invention.

Note that the circuit diagrams shown in FIG. 6 and FIG. 7 areappropriately referenced in the following description of an exemplarydrive pulse applied to an ink jet head during a nozzle recovery processaccording to the present invention.

As shown by the waveform in FIG. 12, line (2), the timing pulse Tp is aregular sequence of pulses t1 to tn having a period T and a prescribedpulse width Pw. Note that this timing pulse Tp is also used for ink jethead drive during a printing process.

The recovery ejection signal Pd shown at FIG. 12, line (1), is input toselector 150 and output to drive signal generator 180 at the nozzlerecovery process. Based on this recovery ejection signal Pd, driver 190applies a drive pulse as shown at FIG. 12, line (3), to ink jet head 30.Ink drops are thus ejected from all nozzles during the nozzle recoveryprocess. Note that the recovery ejection signal Pd of this embodiment isoutput synchronized to the timing pulse Tp with one on pulse outputevery fourth timing pulse Tp.

Note that the drive voltage applied to the ink jet head is indicated bythe amplitude (vertical axis) of the drive pulse shown in FIG. 12 (3).

The drive pulses f1, f2, f3, and f4 output at timing points t4, t8, t12,and t16 are drive pulses causing ink ejection from the nozzles. Thedrive voltage of those drive pulses therefore has the same amplitude VHas a drive pulse used for printing. The amplitude of drive pulses f11,f12, f13, f21, f22, f23, f31, f32, f33, f41, f42, and f43 output at thesame period T as timing pulse Tp between ink ejection drive pulses is anamplitude VL lower than amplitude VH.

As a result of this drive method, the ink jet head is driven three timesat drive pulse VL at the same period T as the timing pulse Tp, and theink jet head is then driven once at drive voltage VH. This operatingsequence, or recovery process unit, is repeated four times.

Driving the ink jet head with low amplitude drive pulses f11, f21, andf13 mobilizes ink inside the nozzles, thereby lowering the ink viscosityat the nozzle tip, and enabling efficient ink ejecting when drive pulsef1 is applied.

It should be noted that the exemplary embodiment of the presentinvention described above applies three low amplitude drive pulsesfollowed by one high amplitude drive pulse in one recovery process unit,and repeats this recovery process unit four times. The invention shallnot be so limited, however, as it will be obvious that variouscombinations of low and high amplitude drive pulses can be usedaccording to the properties of the ink, the interval between nozzlerecovery processes, and other factors.

An alternative embodiment of an exemplary drive pulse used for a nozzlerecovery process according to the present invention is shown in FIG. 13(1).

Before a drive pulse g1 of drive voltage VH for ejecting ink is applied,a drive pulse g11, g12, g13, and g14 of a drive voltage VLL havingpolarity different from that of drive pulse g1 is applied four times.This sequence constitutes one recovery process unit, which is repeatedthree times. Note that this drive wave can be achieved using a circuitas shown in FIG. 7 by setting the voltage V2 supplied to driver 190 bhigher than the voltage supplied to driver 190 a so that VLL=V2−V1.

When an electrostatic actuator is used as the pressure generating meansshown in FIG. 3, driving results in accumulation of a residual charge inthe actuator. This causes a problem unique to an electrostatic actuator,that is, that the diaphragm may not return when the charge between theopposing electrodes is discharged, and the volume of the ink dropsejected from the nozzle then gradually decreases.

The method of the present invention, however, applies drive pulses g11to g14 having polarity opposite that of the drive pulse g1. Applyingthese drive pulses g11 to g14 to drive the head can both mobilize ink inthe nozzle to enable efficient ink ejecting when drive pulse f1 isapplied, and reduce the residual charge accumulated in the electrostaticactuator.

A further alternative embodiment of an exemplary drive pulse used for anozzle recovery process according to the present invention is shown inFIG. 13 (2).

In this example drive pulses f11, f12, and f13 of drive voltage VL areapplied before drive pulse f1 of drive voltage VH is applied to ejectink. After drive pulse f1 is applied, reverse polarity drive pulses g11and g12 of drive voltage VLL are applied to complete a recovery processunit, and this recovery process unit is repeated three times.

As this example illustrates, it is also possible to combine drive pulsesf11 to f13 for mobilizing ink near the nozzles, with drive pulses gilland g12 for both mobilizing ink near the nozzles and reducing theresidual charge accumulated in the electrostatic actuator.

APPLICATIONS IN INDUSTRY

An ink jet printer according to the present invention as described abovecan be used as an output terminal for a computer, a color printingapparatus, and a facsimile machine, and is particularly well suited asan ink jet recording apparatus for use in fields requiring a lowoperating cost and high reliability.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A drive method for an ink jet printer comprisinga plurality of nozzles for ejecting ink drops, a plurality of pressuregenerators each disposed corresponding to a respective one of saidplurality of nozzles for pressurizing ink in said nozzles, and acarriage for transporting said nozzles relative to a printing medium forprinting, said drive method comprising the steps of: generating areference signal having a single frequency; applying to each of saidplurality of pressure generators in synchronism with the referencesignal one of the following: a first electric pulse having a firstamplitude enabling ink drop ejecting, and a second electric pulse havinga second amplitude lower than the first amplitude of the first electricpulse for mobilizing ink inside said nozzles; performing a printingprocess whereby the first electric pulse is selectively applied to atleast a select one of the plurality of pressure generators according torecording content; and performing a nozzle recovery process whereby thesecond electric pulse is applied to at least one of the plurality ofpressure generators a plurality of times, and the first electric pulseis then applied to the at least one of the plurality of pressuregenerators, for preventing nozzle clogging.
 2. The ink jet printer drivemethod according to claim 1, wherein said nozzle recovery process stepof applying the second electric pulse to at least one of the pluralityof pressure generators a plurality of times, and then applying the firstelectric pulse to the at least one of the plurality of pressuregenerators, is repeated at least two consecutive times.
 3. The ink jetprinter drive method according to claim 1, wherein the ink jet printeris a serial ink jet printer printing while moving the nozzles in a shiftdirection, and the nozzle recovery process step is executed at eachprinted line.
 4. The ink jet printer drive method according to claim 1,wherein the nozzle recovery process step is executed after a printcommand is received and before the printing process based on thereceived print command.
 5. The ink jet printer drive method according toclaim 1, wherein each of the plurality of pressure generators comprises:a diaphragm disposed in a part of an ink path in communication with arespective one of said plurality of nozzles; and an electrode opposingthe diaphragm for electrostatically displacing the diaphragm by means ofan applied electric pulse.
 6. The ink jet printer drive method accordingto claim 5, wherein a first polarity of the first electric pulse isdifferent from a second polarity of the second electric pulse.
 7. Theink jet printer drive method according to claim 6, further comprisingthe steps of generating a third electric pulse having the secondpolarity; and applying at least one of the first second and thirdelectric pulses to at least one of said plurality of pressure generatorsin synchronism with the reference signal.
 8. The ink jet printer drivemethod according to claim 1 further comprising the steps of: performingthe printing process whereby the first electric pulse is selectivelyapplied to at least a selected one of the plurality of pressuregenerators according to recording content to eject ink drops from atleast a corresponding one of the plurality of nozzles for printing to arecording medium, and applying a second electric pulse to at least a nonselected one of said plurality of nozzles.
 9. The ink jet printer drivemethod according to claim 1, wherein the ink jet printer comprises aplurality of nozzles grouped according to color for ejecting ink dropsin a plurality of colors.
 10. An inkjet printer having a plurality ofnozzles for ejecting ink drops, a plurality of pressure generators eachdisposed corresponding to a respective one of said plurality of nozzlesfor pressurizing ink in said nozzles, and a carriage for transportingsaid nozzles relative to a printing medium for printing, said inkjetprinter comprising: a reference signal generator for generating areference signal having a single frequency; a driver circuit forapplying to each of said plurality of pressure generators in synchronismwith the reference signal one of the following: a first electric pulsehaving a first amplitude enabling ink drop ejecting, and a secondelectric pulse having a second amplitude lower than the first amplitudeof the first electric pulse for mobilizing ink inside said nozzles; anda controller for controlling said driver circuit, said controllercomprising; means for performing a printing process whereby the firstelectric pulse is selectively applied to at least a select one of theplurality of pressure generators according to recording content; andmeans for performing a nozzle recovery process whereby the secondelectric pulse is applied to at least one of the plurality of pressuregenerators a plurality of times, and the first electric pulse is thenapplied to the at least one of the plurality of pressure generators, forpreventing nozzle clogging.
 11. The ink jet printer according to claim10, wherein each of said plurality of pressure generators comprises: adiaphragm disposed in a part of an ink path in communication with arespective one of said plurality of nozzles, and an electrode opposingsaid diaphragm for electrostatically displacing the diaphragm inaccordance with said driver circuit.
 12. The ink jet printer accordingto claim 11, wherein said driver circuit generates the first electricpulse having a first polarity different from a second polarity of thesecond electric pulse.
 13. The ink jet printer according to claim 12,wherein said driver circuit generates a third electric pulse having thesecond polarity, and wherein said driver circuit applies at least one ofthe first, second, and third electric pulses to at least a selected oneof said plurality of pressure generators in synchronism with thereference signal.
 14. The ink jet printer according to claim 10, whereinsaid driver circuit selectively applies the first electric pulse to atleast a selected one of said pressure generators according to recordingcontent to eject ink drops from a respective one of said plurality ofnozzles for printing to the recording medium, and wherein said drivercircuit applies the second electric pulse to at least one of saidplurality of nozzles other than the respective one of said plurality ofnozzles to which the first electric pulse was applied by said drivercircuit.
 15. The ink jet printer according to claim 10, wherein saidplurality of nozzles are grouped according to color for ejecting inkdrops in a plurality of colors.
 16. The ink jet printer according toclaim 11, wherein each of said plurality of pressure generatorscomprises: a common terminal connected in common to each of saidplurality of pressure generators, and a plurality of segment terminalsconnected individually to a respective one of said plurality of pressuregenerators; wherein said driver circuit comprises: a first drivercircuit for applying the first electric pulse having the first amplitudeto said common terminal; and a second driver circuit for applying athird electric pulse having a third amplitude different from the firstamplitude of the first electric pulse to a selected one of saidplurality of segment terminals, wherein when said driver circuit appliesthe second electric pulse to each of said plurality of pressuregenerators said first driver circuit applies the first electric pulse tosaid common terminal and said second driver circuit applies the thirdelectric pulse to the selected one of said plurality of segmentterminals at substantially the same time.
 17. An ink jet printer havinga plurality of nozzles for ejecting ink drops, a plurality of pressuregenerators each disposed corresponding to a respective one of saidplurality of nozzles for pressurizing ink in said nozzles, and acarriage for transporting said nozzles relative to a printing medium forprinting, said inkjet printer comprising: a reference signal generatorfor generating a reference signal having a single frequency; a drivercircuit for applying to each of said plurality of pressure generators insynchronism with the reference signal one of the following: a firstelectric pulse having a first amplitude enabling ink drop ejecting, anda second electric pulse having a second amplitude lower than the firstamplitude of the first electric pulse for mobilizing ink inside saidnozzles; and a controller for controlling said driver circuit, saidcontroller configured to perform a printing process whereby the firstelectric pulse is selectively applied to at least a select one of theplurality of pressure generators according to recording content; andperforming a nozzle recovery process whereby the second electric pulseis applied to at least one of the plurality of pressure generators aplurality of times, and the first electric pulse is then applied to theat least one of the plurality of pressure generators, for preventingnozzle clogging.
 18. The ink jet printer according to claim 17, whereineach of the plurality of pressure generators comprises: a diaphragmdisposed in a part of an ink path in communication with a respective oneof said plurality of nozzles, and an electrode opposing the diaphragmfor electrostatically displacing the diaphragm in accordance with saiddriver circuit.
 19. The ink jet printer according to claim 18, whereinsaid driver circuit generates the first electric pulse having a firstpolarity different from a second polarity of the second electric pulse.20. The ink jet printer according to claim 19, wherein said drivercircuit generates a third electric pulse having the second polarity, andwherein said driver circuit applies at least one of the first, second,and third electric pulses to at least a selected one of said pluralityof pressure generators in synchronism with the reference signal.
 21. Theink jet printer according to claim 17, wherein said driver circuitselectively applies the first electric pulse to at least a selected oneof the pressure generators according to recording content to eject inkdrops from a respective one of the plurality of nozzles for printing tothe printing medium, and wherein said driver circuit applies the secondelectric pulse to at least one of said plurality of nozzles other thanthe respective one of said plurality of nozzles to which the firstelectric pulse was applied by said driver circuit.
 22. The ink jetprinter according to claim 17, wherein said plurality of nozzles aregrouped according to color for ejecting ink drops in a plurality ofcolors.
 23. The ink jet printer according to claim 17, wherein each ofsaid plurality of pressure generators comprises: a common terminalconnected in common to each of said plurality of pressure generators,and a plurality of segment terminals connected individually to arespective one of said plurality of pressure generators; wherein saiddriver circuit comprises: a first driver circuit for applying the firstelectric pulse having the first amplitude to said common terminal; and asecond driver circuit for applying a third electric pulse having a thirdamplitude different from the first amplitude of the first electric pulseto a selected one of said plurality of segment terminals, wherein whensaid driver circuit applies the second electric pulse to each of saidplurality of pressure generators said first driver circuit applies thefirst electric pulse to said common terminal and said second drivercircuit applies the third electric pulse to the selected one of saidplurality of segment terminals at substantially the same time.